Corrosión en soldaduras de aparatos de ortodoncia

Reaction dynamics of O({sup 1}D) atoms with H{sub 2} molecules was reinvestigated using the crossed molecular beams technique with pulsed beams. The O({sup 1}D) beam was generated by photodissociating O{sub 3} molecules at 248 nm. Time-of-flight spectra and the laboratory angular distribution of the OH products were measured. The derived OH product center-of-mass flux-velocity contour diagram shows more backward scattered intensity with respect to the O({sup 1}D) beam. In contrast to previous studies which show that the insertion mechanism is the dominant process, our results indicate that the contribution from the collinear approach of the O({sup 1}D) atom to the H{sub 2} molecule on the first excited state potential energy surface is significant and the energy barrier for the collinear approach is therefore minimal. Despite the increased time resolution in this experiment, no vibrational structure in the OH product time-of-flight spectra was resolved. This is in agreement with LIF studies, which have shown that the rotational distributions of the OH products in all vibrational states are broad and highly inverted

Wear and corrosion interactions on titanium in oral environment : literature review

The oral cavity is a complex environment where corrosive substances from dietary, human saliva, and oral biofilms may accumulate in retentive areas of dental implant systems and prostheses promoting corrosion at their surfaces. Additionally, during mastication, micromovements may occur between prosthetic joints causing a relative motion between contacting surfaces, leading to wear. Both processes (wear and corrosion) result in a bio-tribocorrosion system once that occurs in contact with biological tissues and fluids. This review paper is focused on the aspects related to the corrosion and wear behavior of titanium-based structures in the oral environment. Furthermore, the clinical relevance of the oral environment is focused on the harmful effect that acidic substances and biofilms, formed in human saliva, may have on titanium surfaces. In fact, a progressive degradation of titanium by wear and corrosion (tribocorrosion) mechanisms can take place affecting the performance of titanium-based implant and prostheses. Also, the formation of wear debris and metallic ions due to the tribocorrosion phenomena can become toxic for human tissues. This review gathers knowledge from areas like materials sciences, microbiology, and dentistry contributing to a better understanding of bio-tribocorrosion processes in the oral environment.(undefined

Corrosion susceptibility of steel drums to be used as containers for intermediate level nuclear waste

The present work is a study of the corrosion susceptibility of steel drums in contact with cemented ion-exchange resins contaminated with different types and concentrations of aggressive species. A special type of specimen was manufactured to simulate the cemented ion-exchange resins in the drum. The evolution of the corrosion potential and the corrosion rate of the steel, as well as the electrical resistivity of the matrix were monitored over a time period of 900 days. The aggressive species studied were chloride ions (the main ionic species of concern) and sulphate ions (produced during radiolysis of the cationic exchange-resins after cementation). The work was complemented with an analysis of the corrosion products formed on the steel in each condition, as well as the morphology of the corrosion products. When applying the results obtained in the present work to estimate the corrosion depth of the steel drumscontaining the cemented radioactive waste after a period of 300 years (foreseen durability of the Intermediate Level Radioactive Waste facility in Argentina) , it is found that in the most unfavourable case (high chloride contamination), the corrosion penetration will be considerably lower than the thickness of the wall of the steel drums

Corrosion susceptibility of steel drums to be used as containers for intermediate level nuclear waste

The present work is a study of the corrosion susceptibility of steel drums in contact with cemented ion-exchange resins contaminated with different types and concentrations of aggressive species. A special type of specimen was manufactured to simulate the cemented ion-exchange resins in the drum. The evolution of the corrosion potential and the corrosion rate of the steel, as well as the electrical resistivity of the matrix were monitored over a time period of 900 days. The aggressive species studied were chloride ions (the main ionic species of concern) and sulphate ions (produced during radiolysis of the cationic exchange-resins after cementation). The work was complemented with an analysis of the corrosion products formed on the steel in each condition, as well as the morphology of the corrosion products. When applying the results obtained in the present work to estimate the corrosion depth of the steel drumscontaining the cemented radioactive waste after a period of 300 years (foreseen durability of the Intermediate Level Radioactive Waste facility in Argentina) , it is found that in the most unfavourable case (high chloride contamination), the corrosion penetration will be considerably lower than the thickness of the wall of the steel drums

Tarnishing and corrosion of silver-based casting alloys in synthetic salivas of different compositions

The aim of this work is to study the electrochemical response of Ag and Ag-based alloys in synthetic salivas of different compositions. The effect of several anions present in saliva on the dissolution of Ag and some of the alloy components, such as Pd and Cu, was evaluated. Potentiostatic and potentiodynamic techniques were used and were complemented with atomic adsorption and XPS analysis. Chloride, fluoride and thiocyanate were particularly analysed because of their aggressiveness. Corrosion, pigmentation and/or tarnishing processes were enhanced when they were present in the synthetic saliva. A dependence of the selectivity of Pd dissolution from Ag–15Pd binary alloy with the potential was noticed. Ag microsegregations and precipitates formed on casting alloys showed higher activity than the matrix and rendered the alloy more susceptibility to deterioration. The need to use a normalised saliva to make comparisons of electrochemical results is highlighted.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Preliminary results of corrosion monitoring studies of carbon steel overpack exposed to supercontainer concrete buffer

The supercontainer (SC) is the reference concept for the postconditioning of vitrified high level radioactive waste and spent fuel in Belgium. It is designed with a concrete buffer completely surrounding a carbon steel overpack. A half-scale (HST-2) experiment was set up to measure the instantaneous uniform corrosion rate, representative of the initial oxic phase, in situ. The test setup has the same diameter as a full size SC, but it is limited in height to approximately half of a real SC. The corrosion rate of carbon steel is measured in four ways: weight loss measurements (carbon steel coupons), corrosion sensor based on linear polarisation resistance, corrosion sensor based on multisine electrochemical impedance spectroscopy and corrosion sensor based on single sine electrochemical impedance spectroscopy coupled to a unique analytical method. This paper presents the preliminary results of the corrosion rates measured with these independent methods.Fil: Kursten, B.. SCK•CEN; BélgicaFil: Druyts, F.. SCK•CEN; BélgicaFil: Areias, L.. SCK•CEN; BélgicaFil: Ingelgem, Y. van. Vrije Unviversiteit Brussel; BélgicaFil: De Wilde, D.. Vrije Unviversiteit Brussel; BélgicaFil: G. Nieubourg. Vrije Unviversiteit Brussel; BélgicaFil: Duffó, Gustavo Sergio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Materiales (CAC); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bataillon, C.. Commissariat à l'Énergie Atomique. Laboratoire d’Etude de la Corrosion Aqueuse; Franci